Fixes #10369.

Change-Id: If0a6d2b33c6862c9f7f862bdc997f2204072c6dc
Reviewed-on: https://go-review.googlesource.com/8620
Run-TryBot: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>